| Popis: |
DC-DC converters used in LED driver applications are desired to operate with high efficiency at high switching frequencies. Class-E resonant converter, which is simple in structure and easy to implement, is especially suitable for high-frequency and low-power applications because the directly grounded switch can operate under soft switching conditions. However, when the input voltage and output power vary over a wide range in variable frequency control, the soft switching conditions are lost. To eliminate this drawback, the class-E resonant converter with synchronous rectifier is proposed as an LED driver. Although designed to operate at the fixed switching frequency, this converter structure is controlled using a hybrid method in which variable and fixed frequency switching techniques are used together because the efficiency decreases as the load becomes lighter. The converter incorporates all the advantages of conventional class-E resonant converter, while the hybrid control highlights the advantageous aspects of both variable and fixed frequency switching. To verify the validity of the driver, a prototype circuit that can operate in the 25–50 V input voltage range and whose load is a 20 W LED module is constructed. A control algorithm where the operating parameters such as switching frequency, duty ratio and synchronization angle of the converter are estimated using the polynomial regression technique is developed for closed-loop control of the driver. The driver is dynamically tested against varying input voltage and reference current across a wide range. Test results confirm the validity and feasibility of the driver, and it is observed that the polynomial regression-based control algorithm effectively and robustly follows the reference current. Furthermore, while power control of the LED module is effectively carried out throughout the entire input voltage range from 0 W to 20 W, the power switches are turned on under soft switching conditions. |
